As a method for producing aminobenzopyran compound, there is known a method of reducing the corresponding nitrobenzopyran compound with iron (see, for example GB 1,121,307). The method, however, occurs a large quantity of iron waste and further is liable to do damage to reactors. In addition, the method has disadvantages in procedures (filtration, transfer, stirring or washing), and therefore it has many problems for applying to the production of pharmaceuticals or pharmaceutical intermediates for which a high level of quality control is required. Further, although hydrazine reduction by using FeCl3-6H2O and active carbon as a catalyst (J. Org. Chem., Vol. 50, No. 25, 5092 (1985) and a reduction with tin (Sn)-hydrochloric acid (Org. Syn. Coll., Vol. 1, 455 (1941) are proposed, these methods have problems in aspects of reaction selectivity or toxicity.
If reduction of nitro group is merely required, some methods such as catalytic reduction or the like are known, in which 2,2-dimethyl 2H-1-benzopyran compound being a substrate contains olefin bonds, and it is required to acquire a high selectivity with the bonds. Similarly, a high selectivity with olefin bonds is required in hydrazine reduction by using FeCl3-6H2O and active carbon as a catalyst.
The present inventors, as results of eager investigation, found a method for producing aminobenzopyran compound, which has a high selectivity with olefin bonds, provides intended compounds in a high yield, and further necessitates a simple work-up procedure, results in little wastes and has no influence on reactors, and they consequently completed the present invention.